The U.S. Chamber of Commerce dramatically expanded the 2010 House field for Republicans by battering their Democratic opponents early on with hard-hitting television ads, a new post-election analysis by a union-backed group shows.

“The U.S. Chamber of Commerce played a central strategic role in a coordinated effort to elect Republicans in this fall’s elections,” the new U.S. Chamber Watch study concludes. “Anonymously funded by the largest corporate special interests in the world, the U.S. Chamber led the charge to increase Republican seats in the Congress by orchestrating the unprecedented amounts of money conservative groups marshaled for that purpose.”

A chamber spokesman said his group backed candidates who support the business community.

“The Chamber was very clear from the beginning of this year that we intended to launch the largest voter education and issues advocacy effort in our history,” chamber spokesman J.P. Fielder said in an e-mail to Roll Call. “We did this not to support Republican or Democrat candidates, but to support pro-business candidates.”

Fielder added that the “election was a referendum on the economy and our voter education efforts highlighted where candidates stood on policies that create or stifle job creation.”

According to an advanced copy of the report provided exclusively to Roll Call, the chamber spent $32 million on the 2010 midterm elections, 93 percent on GOP candidates. The business group also worked “alongside 30 conservative groups, including American Crossroads and Crossroads GPS” — two groups run by former Bush administration adviser Karl Rove — an alliance that the report says “reflects [the chamber’s] overall mission to elect a Republican Congress.”

“It worked almost exclusively to elect Republicans in the powerful Senate, giving one lone endorsement to a Democrat, West Virginia’s Joe Manchin, on whom it made no expenditures. On the House side, the chamber created an appearance of bipartisanship by spending on behalf of eleven Democrats,” the 11-page report states. “But the chamber’s support for Democratic members was razor-thin, and sometimes, the chamber withheld support altogether, even where Democratic members worked hard to earn the chamber’s approval. On average, the Chamber spent 18 percent as much on Democratic candidates as it did on Republican House candidates it supported.”

Fielder said the chamber didn’t determine its support from party labels.

“We have an accurate yardstick to measure where candidates stand on pro-growth policies, and it’s our How They Voted Scorecard,” Fielder said in his e-mail. “This doesn’t measure Rs or Ds, but looks at how candidates vote on issues impacting the businesses, America’s job creators.”

U.S. Chamber Watch was founded in May by Change to Win, a labor federation that includes the International Brotherhood of Teamsters and Service Employees International Union. Labor unions and the chamber are often at odds over legislative issues.

In Senate races, chamber-backed candidates went 9-4 after it spent nearly $20 million helping GOP candidates, according to the new report. In the House, the chamber’s record with Republicans was 26-13, with one race still undecided.

The U.S. Chamber Watch’s study also says that although the chamber spent $9 million to help elect GOP House members, it spent less than $2 million on Democratic House candidates.